1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head for writing data on a magnetic recording medium with the coercivity thereof lowered by applying near-field light thereto, and a manufacturing method for the thermally-assisted magnetic recording head.
2. Description of the Related Art
With recent increases in recording density of magnetic recording devices such as magnetic disk drives, there has been demand for improved performance of magnetic heads and magnetic recording media. In a magnetic disk drive, a magnetic head is provided in the form of a slider configured to slightly fly over the surface of a magnetic recording medium. Typically, the magnetic head of such a form includes a head body having a medium facing surface for facing the magnetic recording medium, and a protective film for protecting the medium facing surface of the head body. The head body includes the principal components of the magnetic head.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the magnetic recording medium smaller. Making the magnetic fine particles smaller, however, disadvantageously lowers the thermal stability of magnetization of the magnetic fine particles. To overcome this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the magnetic recording medium, thereby making it difficult to perform data writing with existing magnetic heads.
As a solution to the problems described above, there has been proposed a technology called thermally-assisted magnetic recording. The technology uses a magnetic recording medium having high coercivity. When writing data, a write magnetic field and heat are applied almost simultaneously to the area of the magnetic recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the magnetic recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with light. The light to be used for generating near-field light is typically guided through a waveguide, which is provided in the head body, to the plasmon generator provided in the head body near the medium facing surface.
The light to be used for generating near-field light can be supplied to the waveguide by, for example, fixing a light source onto the head body and causing the light emitted from the light source to enter the entrance end of the waveguide, as disclosed in U.S. Pat. No. 8,861,318 B1, U.S. Patent Application Publication No. 2015/0194172 A1, and JP 2007-188583A.
In a thermally-assisted magnetic recording head, the plasmon generator gets hot due to heat generated by itself during write operation. As a result, the plasmon generator expands, or shrinks by aggregation. The thermally-assisted magnetic recording head may thus suffer from damage to part of the protective film near the plasmon generator due to the heat generated by the plasmon generator or due to a deformation of the plasmon generator caused by the heat.
U.S. Pat. No. 8,861,318 B1 discloses one of solutions to the foregoing problem. More specifically, U.S. Pat. No. 8,861,318 B1 discloses a thermally-assisted magnetic recording head including a waveguide, a magnetic pole, a plasmon generator, a first protective film and a second protective film. The waveguide has a first end face located in the medium facing surface. The magnetic pole has a second end face located in the medium facing surface. The plasmon generator has a third end face located in the medium facing surface. The first protective film covers the second end face. The second protective film covers the first end face and the third end face. The first and second protective films, in combination, will be collectively referred to herein as the overall protective film.
According to the thermally-assisted magnetic recording head disclosed in U.S. Pat. No. 8,861,318 B1, the second protective film has higher heat resistance than the first protective film. This makes it possible to prevent damage to the second protective film, which covers the third end face of the plasmon generator.
Further, U.S. Pat. No. 8,861,318 B1 describes a method for forming the overall protective film as follows. First, the first protective film is formed to cover the medium facing surface. Then, a photoresist film is formed to cover the first protective film. Then, light is projected onto the entrance end of the waveguide, and the photoresist film is exposed to the light having passed through the waveguide to thereby form an exposure region on the photoresist film. The exposure region is then etched to form an opening in the first protective film. Then, the second protective film is formed to fill the opening.
The above-described method has a disadvantage in that part of the light projected onto the entrance end of the waveguide passes through a part of the head body other than the waveguide and reaches the photoresist film to cause the photoresist film to undergo unwanted exposure at a region thereof not intended to be the exposure region, thus resulting in reduced reliability of the overall protective film.
U.S. Pat. No. 8,861,318 B1 describes a technique to form a light shield to be adjacent to the magnetic pole. However, the technique cannot overcome the aforementioned disadvantage.